Compact, folding rain umbrellas and, more particularly, multiple fold umbrellas have a more complex frame structure, composed of many ligaments or ribs, as compared with foldable umbrellas having only a single fold. Folding umbrellas are particularly susceptible to breakage, especially those of the multiple fold design. Even a moderate wind force acting on the protective fabric of the umbrella will force the umbrella to invert since the force, although moderate, acts on a large surface area, much like the sail of a boat. This force is transferred to the frame structure supporting the protective fabric, causing the ribs to bend as they absorb this force. Ribs formed entirely of a non-elastic alloy, such as aluminum or steel, which experience such bending, remain distorted due to their lack of resilience and do not return to their original unbent shape, and thereby distort the entire support frame and degrade the normally smooth opening and closing operations of the umbrella. On the other hand, forming ribs of a material which is too flexible yields an umbrella which will invert too easily making it cumbersome and annoying to the user. The above problems affect all folding umbrellas and are more severe in the case of the multiple fold category.
Therefore, a design is needed to provide ribs having a proper balance of rigidity and flexibility sufficient to reduce inversion to an acceptable minimum, while providing sufficient elasticity to return the ribs back to their original shape in the event of an inversion.